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Sputtering targets
can be simply clamped to the sputter source cathode inside
the sputter deposition system. However, this procedure can
prove costly due to cracking, warping or other damage to the
target in use caused by inadequate cooling. Wherever possible,
it is good practice to bond the sputter target to a strong,
compatible backing plate.
Target bonding is
a critical process and the exact fabricating method employed
can vary depending on the choice of the sputtering target
material. A properly bonded sputtering target will normally
give a longer working life than a non-bonded target, may enable
the use of a higher power input to achieve faster sputtering
rates and will enable thin film process parameters to be consistently
repeated.
All metallic bonded
targets include a sputtered metal intermediate bonding layer
on the "bonded" side of the target, which acts as
a barrier layer protecting the target material integrity from
diffusion of the hot primary bonding metal alloy. The metal
bonding technology offers excellent thermal and electrical
conductivity and is compatible with either DC or RF power
supplies. A properly bonded target will stay adhered to the
backing plate providing there is a continuous supply of sufficient
cool water and the sputtering source cathode is not over powered.
Shear stresses that
develop between the target and backing plate, due to heating
during sputtering, can be a cause of bonding failure when
the backing plate and target materials do not have compatible
coefficients of thermal expansion. Depending on the dimensional
tolerances allowed, the bond thickness can be adjusted to
help compensate for these stresses.
Silver-Filled
Epoxy
The silver filled
epoxy bonding cements are high quality products which have
been readily accepted as having acceptably low outgassing
characteristics. They contain over 90% of high purity silver
for optimum thermal and electrical conductivity.
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